1. Field of the Invention
The present invention relates to a sheet conveying apparatus for conveying a sheet in a predetermined direction.
Here, the "sheet" in this disclosure includes, for example, a recording sheet on which an image or images are recorded or printed, and an original sheet having an image or images to be read. The sheet conveying apparatus according to the present invention can be applied to image recording apparatuses, image reading apparatuses, document feeding mechanisms or the like. More particularly, the present invention is applicable to facsimile machines, copying machines, printer apparatuses, word processors, electronic typewriters and the like.
2. Related Background Art
In the past, each of printer machines, facsimile machines and the like included a sheet feeding mechanism for feeding out sheets one by one, as needed, from a sheet stack. Such a sheet feeding mechanism is generally constituted by pick-up rollers for picking up a sheet and sheet feeding rollers for feeding out sheets one by one, and the sheet is fed by rotating these rollers under the control of a control circuit.
Accordingly, in the conventional sheet feeding apparatuses, it was necessary to include, at least, a motor for rotating pick-up rollers, which is controlled and driven by a control circuit and a driving circuit, and a sheet feeding motor, or an electro-magnetic clutch and motor which are directly driven by a control circuit and a driving means.
However, with such construction, since the exclusive motors were provided for the pick-up rollers and sheet feeding rollers, respectively, the control means and the driving circuits had to be prepared for each of the motors, thus making the whole system complicated, large-sized and expensive.
An example of the conventional sheet conveying apparatus utilized in a sheet discharging section is shown in FIGS. 7A-7E. FIGS. 7A and 7C are plan views of the conventional sheet conveying apparatus for discharging the sheet, and FIGS. 7B, 7D and 7E are side views of such sheet conveying apparatus. As shown, the conventional sheet conveying apparatus arranged in the sheet discharging section includes discharging rollers 203 comprising a plurality of high friction rubber rollers substantially equidistantly arranged on a shaft or core bar 207, and discharging members 209 (FIG. 7A) or discharging springs 201 (FIG. 7C) arranged on a support 202 and protruding toward the core bar 207 between the rollers 208.
In the sheet conveying apparatus so constructed, when the discharging rollers 203 are rotated in a direction a which corresponds to a sheet conveying direction, since the discharging rollers 203 do not contact any members, the rollers can rotate without any load. Here, when a sheet S is supplied from a direction b by means of an appropriate sheet supplying mechanism (not shown) and the end of the sheet S is fed to a pinching position between the discharging rollers 203 and the discharging members 209 (FIG. 7A) or the discharging springs 201 (FIG. 7C), a driving force will act on the pinched end of the sheet, because the pressing force to rotating rollers 203 acts on the sheet at the discharging members 209 or springs 201, thus applying the frictional driving force to the sheet S.
However, in the conventional sheet conveying apparatus mentioned above, there is a problem that the sheet may be jammed when a thin sheet is used, or the sheet can not be fed out when a thick sheet is used.
That is to say, when the sheet S shown by an alternate long and short dash line in FIGS. 7A-7D is thin, since the sheet is weak and there has not enough rigidity to endure the discharging rollers 209 or discharging spring 201, the sheet may be deformed in a wave shape. Consequently, in this case, the deformed sheet may be jammed between the discharging rollers and the discharging members or springs. On the other hand, when the sheet S is thick and has high rigidity, as shown in FIG. 7E, the discharging springs 201 may be deflected excessively by the thick sheet since the spring force can not overcome the rigidity of the sheet, with the result that the sheet S to be fed may not contact the discharging rollers 203. Accordingly, in this case, even when the discharging rollers 203 are driven, the driving force does not act on the sheet, whereby the sheet can not be discharged.